[flang]Add vscale argument parsing (#67676)

Support for vector scale range arguments, for AArch64 scalable vector
extension (SVE) support.

Adds -msve-vector-bits to the flang frontend, and for flang fc1 the
options are -mvscale-min and -mvscale-max (optional). These match the
clang and clang cc1 options for the same purposes.

A further patch will actually USE these arguments.